Connected: An Internet Encyclopedia
RFC 1812 - 5.3.5 Forwarding of Internet Layer Broadcasts

Top: Connected: An Internet Encyclopedia
Up: Requests For Comments
Up: RFC 1812
Up: 5. INTERNET LAYER - FORWARDING
Up: 5.3 SPECIFIC ISSUES
Prev: 5.3.4 Forwarding of Link Layer Broadcasts
Next: 5.3.5.1 Limited Broadcasts

### 5.3.5 Forwarding of Internet Layer Broadcasts

There are two major types of IP broadcast addresses; limited broadcast and directed broadcast. In addition, there are three subtypes of directed broadcast: a broadcast directed to a specified network prefix, a broadcast directed to a specified subnetwork, and a broadcast directed to all subnets of a specified network. Classification by a router of a broadcast into one of these categories depends on the broadcast address and on the router's understanding (if any) of the subnet structure of the destination network. The same broadcast will be classified differently by different routers.

A limited IP broadcast address is defined to be all-ones: { -1, -1 } or 255.255.255.255. A network-prefix-directed broadcast is composed of the network prefix of the IP address with a local part of all-ones or { <Network- prefix>, -1 }. For example, a Class A net broadcast address is net.255.255.255, a Class B net broadcast address is net.net.255.255 and a Class C net broadcast address is net.net.net.255 where net is a byte of the network address.

The all-subnets-directed-broadcast is not well defined in a CIDR environment, and was deprecated in version 1 of this memo.

As was described in Section [4.2.3.1], a router may encounter certain non-standard IP broadcast addresses:

- 0.0.0.0 is an obsolete form of the limited broadcast address

- { <Network-prefix>, 0 } is an obsolete form of a network-prefix- directed broadcast address.

As was described in that section, packets addressed to any of these addresses SHOULD be silently discarded, but if they are not, they MUST be treated according to the same rules that apply to packets addressed to the non-obsolete forms of the broadcast addresses described above. These rules are described in the next few sections.

5.3.5.1 Limited Broadcasts
5.3.5.2 Directed Broadcasts
5.3.5.3 All-subnets-directed Broadcasts
5.3.5.4 Subnet-directed Broadcasts

Next: 5.3.5.1 Limited Broadcasts

Connected: An Internet Encyclopedia
RFC 1812 - 5.3.5 Forwarding of Internet Layer Broadcasts